It's fully lit up! ✨
It took a while, but I finally fixed it (≧∀≦)ノ
I tried to fix it before and accidentally burned out the wiring, so I disassembled part of it and rewired it (lol). It's possible because it's an old kit with a clamshell design, or rather it's easy to do, but it would be difficult with the current kits that are solid inside...
I'm never doing this kind of modification again (ヾﾉ・∀・｀)

Old kit 1/100 Zaku II (Black Tri-Stars) | 水田貴志's Gunpla works